Apparatus for simulating aircraft control loading and feel



Sept. 3, 1957 P. E. GRANDMONT 2,304,698

APPARATUS FOR SIMULATING AIRCRAFT CONTROL LOADING ANO FEEL original Filed July a, 195o 2 she`etssheet 1 1:4 ATTORNEY Il ....11 ....fbll v ...,7....:..` III..

' Sept. 3, 1957 p. E. GRANDMONT Y 2,804,698

APPARATUS FOR SIMULATING AIRCRAFT CONTROL LOADING AND FEEL Original Filed July 8; 1950 2 Sheets-Sheet 2 v INVILNTOR f? @Mfm United States Patent O APPARATUS FR SWULATlNG AIRCRAFT CONTROL LUADiNG AND FEEL Paul E. Grandmont, Bloomfield, N. I., assigner to Curtiss- Wright Corporation, a corporation of Delaware Continuation of appiication Serial No. P72356, .iuiy 8, 1950. This application May 23, 1955, Serial No. 510,119

Claims. (Cl. 35i-12) This invention relates to Hight training apparatus and particularly to means for realistically simulating the operation and "feel of the controls of aircraft under varying Hight conditions.

This application is a continuation of my copending application Serial No. 172,756 Hled July 8, 1950, now forfeited, for Apparatus for Simulating Aircraft Control Loading and Feel.

It has been proposed to apply to the respective simulated aircraft controls of grounded Hight trainers, forces variable according to the simulated airspeed and the control displacement, one example being a motor-tensioned spring arrangement for opposing the control pressure applied by the student pilot. The controls so loaded are intended to simulate in operation actual aircraft controls, namely the aileron, elevator and rudder controls which tend to be centered by air resistance at the control surfaces, this resistance being primarily a function of airspeed. In general the prior art devices are complicated and not sutciently accurate throughout the required range of operation to make realistic the control feel for certain types of aircraft, particularly the high-speed aircraft wherein a greater degree of Hdelity in control loading simulation is required within a narrow range near the neutral position of the control. That is, in a case of highspeed aircraft the air resistance loading for comparatively small control displacements may be considerable and the normal range of control movement is restricted as compared with low-speed aircraft. Also, in the prior art devices the control feel may be unnatural by reason of inertia effects, servo response and related factors.

The feel of the controls therefore during simulated Hight maneuvers involving variable factors such as rapidly changing control displacement, varying airspeed and aircraft attitude, becomes an increasingly important feature in pilot training as the rated speed of the aircraft increases.

A principal object therefore of the present invention is to provide for all types of Hight trainers improved control loading apparatus that is accurate in simulation of the control loading feel for widely varying operation of the controls and that is simple, direct acting and rugged in construction.

Another object of the invention is to provide improved control loading means including electrical means jointly controlled according to simulated Hight conditions, control displacement and control movement for energizing a low-enertia electric torque motor that in a preferred embodiment of the invention is directly connected to said control.

A further object of the invention is to make more realistic the control load feel by introducing in the computation of simulated aerodynamic forces acting on the controls velocity and acceleration factors relating to the movement of the controls per se.

The invention will be more fully set forth in the following description referring to the accompanying drawings,

and the features of novelty will be pointed out with parl 2,8H4,698 Patented sept. 3, 1957 ticularity in the claims annexed to and forming a part of this specification.

Referring to the drawings,

Fig. 1 is a block schematic illustration of components of a control loading system for grounded Hight trainers embodying the present invention;

Fig. 2 illustrates diagrammatically an electrical system used in a preferred form of the invention;

Fig. 3 is a perspective view, partly in section and partly broken away, illustrating a mechanical arrangement of the simulated aircraft controls and control loading apparatus;

Fig. 4 illustrates an alternative form of torque reduction apparatus that may be used in place of the reduction gearing indicated in Figs. 2 and 3; and

Fig. 5 illustrates graphically certain control response characteristics of servo apparatus of the type shown in Fig. 2.

In the schematic illustration, Fig. 1, there is indicated Hight computing means for producing control quantities such as voltages for use in the control force or load computing system. The Hight computing means indicated as the Hight computer is controlled according to manipulation of the various simulated Hight controls by the student pilot, and also according to characteristics of the simulated aircraft, for operating simulated Hight instruments on the instrument panel and, as above-indicated, for producing aerodynamic control quantities for control loading purposes. The Hight computer per se is not a part of the present invention and may for example be of the type disclosed in Patent No. 2,731,737 granted January 24, 1956 to Robert G. Stern for Aircraft Training Apparatus for Simulating Landing and Related Maneuver-s. Briey, the Hight computer is of the electronic type and comprises a number of inter-related electric servo systems, each of which is operable to represent a simulated Hight condition such as airspeed, rate of pitch, pitch attitude, angle of attack, roll, side-slip, yaw, etc. The .servo systems are electrically interconnected so as to respond to control voltages derived from the operation of the respective simulated aircraft controls, namely the aileron,

elevator, rudder, throttle, trim, etc., controls according v to the basic equations of Hight. Function potentiometers are adjustable by the respective motor in each servo system for deriving function voltages for Hight computing, instrument indication, etc.; for example, a potentiometer of the airspeed servo system may be energized by a fixed voltage and adjustable by the airspeed servo motor for deriving a voltage corresponding to the simulated airspeed, or to a function thereof such as the square of airspeed, depending on the potentiometer design. This derived voltage in turn may energize a potentiometer of the angle of attack servo system so that the derived voltage from this potentiometer represents a combined function of both airspeed and angle of attack. By this means, control voltages representing Hight condition and aerodynamic factors can be obtained from the Hight computer for various purposes such as the control loading computations of the present application.

The control loading system for computing and applying a loading force to the respective Hight controls is illustrated by way of example in connection with the elevator stick control 10 located in the pilots cockpit or station. This control loading arrangement, hereinafter described in more ldetail is substantially duplicated for the rudder and aileron controls so that a single description thereof is sutlicient.

A typical grounded Hight trainer station for a student pilot is shown by Fig. 3 wherein simulated stick and rudder controls 10 and 11 are mounted for movement in the p usual manner on a supporting base or platform 12. A

3 single rudder control is shown in the interest of simplicity as it will be understood that the rudders are interconnected as in practice. The pilots seat 13 is also mounted on'the base v12 in proper space relation to .thesimulated controls. l i

The stick which combines vthe Velevator and aileron control functions in a single control, is mounted in conventional manner for universal movement by means of a yoke 14 which carries a transverse `rod'1 5on which the stick 10 is rotatably mounted for forward and aft movement, thereby simulating the elevator control. The yoke 14 is in turn integrally connected to a centrally positioned rod 16 that is journaled in a'bearing'y 17 supported by the base 12 so that'the stick'also is'.fr' ee to rotate transversely in right and left directions thereby simulating aileron control. The rudder 11 is connected to afrod '18 pivotally mounted on the base 12 by Vmeans of the bearing 19 for fore and aft rocking movement thereby simulating rudder control. t

In accordance with the present invention theforce applied to -a respective control in simulation of control loading is produced by a torque devicethat is preferably directly connected through mechanical or equivalent nonelastic connections to the aforesaid control. As shown in a preferred embodiment of the invention, Figs. 2 and 3,"theV torquedevice comprises in the case of .eachV control a low-inertiaelectric torque motor directly connected through suitable reduction gearing and linkages .to `the respective control. When the control stick for example is moved bythe pilot away from neutral, the torque motor produces .torque tending to return the stick to neutral. The motor and gearing may be included in single respective units lindicated at 20, 21 and 22 for the aileron, elevator and rudder controls respectively. The aileron ur1i t`20 for example, comprises a suitable torque converter such as a reduction gearbox a, a motor-generator set 20b including a torque motor and one or more generators, and a position (9) potentiometer 20c. A crank 25 Which is secured to the yoke shaft 16 is connected by means of a link 26 to the Acrank 27 that is in turn connected to the Vreduction gearing in the gear box 20a, so that a force can be directly transmitted between the torque motor and the control stick 10 when aileron control is simulated. In order to'maintain a substantially linear relationship between the input torque voltage and the torque actually felt at the control, suitable linkage is Vused such as a parallelogram arrangement illustrated. The torque units 21 and. 2.2 are .Sirrlilar to mit 2.0 and are Similarly conf nected to the respective elevator and rudder controls by means gf .links 28 and 29- kA simulated trim control 30 is mounted adjacent to the pilots seat and includes elements 31, 32 and 33 pivoted within the unit for simulating elevator, rudder and aileron trim controls. The trirn element 31 for example is operatively connected to a slider contact 34 of a potentiometer 35, Fig. 2, hereinafter described for deriving a voltage corresponding in sense and magnitude to the trim desired.

An alternative arrangement that may be used instead of the reduction gearing for the purpose of minimizing gear noise and back-.lash due to geartolerances is schel matically illustrated by Fig. 4 wherein the stick 10, for example, is connected tothe motor generator 21b for the elevator control through a hydraulic torque reduction means 40. Specifically, the stick extension 10' is'connected to a piston 41 operable within a large diameter cylinder-42 through a'link 43, walking beam'44 and the piston rod 45. The cylinder 42 is connected at its opposite endsby lluid passages 46 and 47 to the opposite ends of a comparatively small diameter elongated cylinder' 48 having a'piston 49 that in turn is connected to the torque motor of unit 2lb through the piston rod 50, rack 51 and pinion 52. The hydraulic medium in the unit 40 can conveniently be oil or an equivalent medium. With this arrangement, torque change between the stick and torque motor can be accomplished smoothly by reason of the uid coupling between the pistons 41 and 49.

The factors involved in the energization of the torque device or motor are diagrammatically indicated in Fig. l wherein the electrical control quantities are represented as having solid line input and output connections, and mechanical transmission is represented by dotted lines. Thus, the stick 10, when used for elevator control, vis directly connectedto the torque device 2lb. The mechanical output of the torque device 2lb can, if desired, operate a suitable torque measuring device 21d for ,producing a feedback control quantity for the torque device in order to insure linear response of the torque device to its input control quantity. lfthe characteristics of the torque device are such that the torque output has a linear relation to the control quantity or voltage input the torque measuring device need not be used. l

The torque device is controlled in the present instance by a voltage produced by the elevatorforce computer 80, A s illustrated by Fig. 2, the force computer inputs include factors representing primarily functions of airspeed (from the Hight computer), trim, and actual displacement of the control by the pilot (from the potition potentiometer `21d Vshown as mechanically adjustable by the stick), which are modified by secondary dynamic factors which are functions of the velocity (w) and acceleration (a) of the output shaft of the torque device indicated by the mechanical connection or shaft 23. The velocity and acceleration feedback devices 65 and l68 are mechanically connected to and driven by the shaft 23 as indicated.

The ight computer also produces control voltages which are functions of airspeed for similarly designed rudder and aileron force computers and also a voltage that is a function of airspeed for the respective elevator, rudder and aileron position potentiometers, the elevator position potentiometer 21C being illustrated as energized by such a voltage.

Referring specifically to Fig. 2, the various inputs for the elevator force summing amplifier 55 are indicated as connected through suitable resistances to a common junction point that is in turn connected in well-known manner to the electronic circuits of the summing amplifier, The inputs from the flight computer (as are all irnputs to the summing amplifier) are represented as alternating Vcurrent voltages, depending in phase on the sense of the particular control voltage. The elevator force computer inputs from the tlight computer indicated at 56 may for example represent a combined function of the simulated angle of attack and airspeed squared, it being apparent that angle of attack is a pertinent factor for determining in combinationpwith airspeed the air resist-V ance acting on the control surfaces. Where desired, the elevator force computation can be made more precise by including additional inputs indicated at 57 which for example may be functions of Mach number, etc. In general, the factors for computing the elevator loading force include power effect, elevator deflection, angle of attack, pitching velocity, trim tab adjustment, and flap position. All, or the more important of these factors can be used in the loading force computation depending on the degree of precision required. The rudder factors are primarily side-slip, rudder deflection and trim, and the aileron factors are primarily rate of roll, aileron deflection and trim and angle of attack. Each factor may take the form of a coefficient that is multiplied by a constant and the square of indicated airspeed.

The trim control input at 58 is derived from the trim potentiometer 35 through conductor 5S' by means of the manually adjustable slider contact 34. As previously Y indicated, the pilot positionsV the trim element 31 so as indicated airspeed squared and is grounded at its midpoint so that the voltage derived at contact 34 can vary both in sense and in magnitude for representing positive or negative trim.

The input at 59 from the position (0) potentiometer 21C is connected by conductor 59 to the slider contact 77 of the or elevator position potentiometer 21C. This potentiometer, as in the case of the trim potentiometer, is energized at its opposite terminals by oppositely phased voltages representing indicated airspeed squared and is grounded at its mid-section so that the derived voltage can be of different sense and varying magnitude to represent positive and negative displacement of the elevator from the neutral position.

The inputs so far described when algebraically summed by the force summing amplifier S are sutiicient in themselves to define a steady loading force acting on the control stick in opposition to the pilots control pressure. However, the feel of the stick will not be natural, particularly in the case of rapid and extended control movements. The electrical system illustrated in Fig. 2 provides both viscous damping and inertia factors for simulating to a realistic degree the control feel. f

The algebraically summed and amplified output of the force summing amplifier energizes the torque device generally indicated at 2lb. Specifically the output energizes the control winding 62 of a two-phase torque motor 63, the secondary winding 64 of the motor being energized from a source of reference A. C. voltage Esc. The torque motor 63, which is preferably of the low power type having a rotor of small inertia, is indicated as directly connected through its shaft to the shaft 23 of the gear box, which in turn is directly connected to the control stick. This type of torque motor has a substantially linear relationship between voltage input and torque output within practical operating limits.

For the purpose of introducing the aforesaid dynamic factors in the computation of the loading force, a pair of generators 65 and 68 each of which have rotors of small inertia, are driven directly by the torque motor 63 as indicated for providing velocity and acceleration feedback respectively. The generator 65 is of the alternating current two-phase type having a reference winding 66 energized from a source of reference A. C. voltage Eze, and an output winding 67 that is connected through conductor 69 to the amplifier input 6?. The input, Ew represents velocity feedback and serves to provide a damping factor for the torque servo motor 63. The phase of the generated voltage in the output winding 67 is opposite to that of the control voltages from the ight computer so that the damping force tends to decrease as the generator velocity decreases. In lieu of generator 65, the feedback voltage may lbe derived by including the motor winding 62 in a bridge circuit and obtaining part of the motor counter E. M. F. from the bridge output terminals in accordance with well-known practice.

This type of damping is graphically illustrated by Fig. 5 wherein the curve 00 (3) is damped according to properly designed feedbackV control. The ordinate 0 represents the stick or control displacement, and the abscissa t represents the time required for the servo system to reach a stabilized condition for a displacement 0i by the student. The curve 00 (l) represents overdamping wherein the control is extremely sluggish in reaching a stable condition, and the curve 90 (3) represents a greatly underdamped condition wherein the control oscillates for a time with gradually decreasing intensity until finally becoming stabilized. Thus, the velocity generator 65 serves to simulate viscous damping of the control. This factor is inherent in the control of actual aircraft, particularly at very low or zero airspeed due to the air-farming motion of the control air foils.

Y The acceleration feedback means comprises in the present instance a generator 68 of the D. C. type and a resistance-capacitance differentiating network and modulator as indicated. The generator output is fed to a low-pass lter 78 and then to a network and a modulator where it is transformed into alternating current for use in the force summing amplifier. This circuitry is generally indicated at 68a in Figs. l and 2. It will be understood that any means suitable for acceleration sensing can be used in place of the D. C. generator and modulator combination.

Referring again to Fig. 2, the output of the low-pass filter is connected to a time-constant or differentiating circuit comprising a condenser 69 and resistance 70, and the output of this differentiating circuit is connected to the movable contact 72 of a chopper as known in the trade, comprising a solenoid 71 that is periodically energ-ized according to the reference A. C. frequency for vibrating the movable contact 72 between the contacts 73, and 74. The contacts 73 and 74 are in turn connected to the opposite terminals of a transformer primary winding 75. The transformer secondary winding 76 is connected through conductor 61 to the amplifier input 61 which represents the acceleration feedback Ea. The phase of this acceleration voltage is related to that of the iiight computer control voltages, so that inertia forces are in effect matched to those of actual aircraft. The differential circuit including the condenser 69 and resistor 70 is connected to a load impedance suciently high so that it has no appreciable loading effect on the output of the differential circuit. This relationship depends on the transformer input reactance Iat 75 being much higher than the impedance of the resistor 70.

It will now be seen that the mechanical inertia of the system including the motor and generator rotors, shafts, gears, etc., can be compensated as desired by adjusting the output of the acceleration feedback generator 68. For example, when the controls of a small light-weight airplane are being simulated, the inertia effect can be minimized. Corresponding adjustment, such as for increased inertia, can be made in the case of simulated controls for heavier planes by reversing polarity of acceleration feedback.

The operation of the system is as follows:

Assuming that the flight computer is operative to produce control force voltages according to indicated airspeed squared and the student pilot has adjusted the trim control 31, Fig. 2, so as to compensate for nose or tail heaviness of the simulated flight, the torque motor 63 is normally positioned at a neutral point corresponding to the trim position, thereby establishing the neutral position of the stick 10. When the stick is in this neutral position, the current in the torque motor control Winding 62 is zero (since the flight computer voltages at 56 and 57 are balanced by the trim and stick position voltages at 58 and 59) and the motor 63 is de-energized so that it exerts no torque whatever on the stick. By way of example, suppose that the trim is further adjusted so to move the slider contact 34 toward the right, as shown in Fig. 2. The resulting derived voltage at the input 58 now unbalances the inputs so that a resultant control current flows through the motor winding 62, the phase relationship of the voltage causing the torque motor in this case to exert a force on the stick 1i) tending to move it in a counter-clockwise direction. If the stick is unrestrained, it will in assuming a new position of balance actuate the slider contact 77 of the position potentiom- H eter 21e sothat the new derived voltage from this potentiometer serves as an answer voltage to the trim voltage for restoring balance of the force amplifier inputs thereby to de-energize the servo system at the new position of balance.

If now the stick 10 is displaced by the pilot, as for example, to the right in Fig. 2 for a climb, the ight computer voltage at 59 is increased from the position potentiometer 21C, the magnitude of this voltage also depending on the simulated indicated airspeed. As the elevator position changes, the angle of attack of the aircraft also changes, thereby varying the 'voltage input at 56 for modifying thecontrol loading force according to aerodynamic principles. The 'amplifier output now tends 4to operate the torque motor 63 'back to the neutral 'position kagainst the pressure applied tothe stick bythe pilot, the magnitude of this restoring force being dependent, as will be seen by inspection, upon the simulated airspeed and the amount of displacement, and hence derived 'voltage Vfrom the potentiometer 21e. Thus, if the Vpilotattempts to hold back the st-ick through"a large angle 0 for a sharp 'climb at comparatively high simulated airspeed, the combined inputs principally at 59, are of such magnitude that the resultant force transmitted'by the torque motor 63 reaches a very high value.

The same considerations apply not only in the case of a'reverse displacement of the stick for a dive, but also in the case of the aileron and' rudder controls above referred to. That is, when the Vcontrol passes through its neutral position, the phase relationship of the position or 0 potentiometer voltages is reversed so that the torque Amotor 63 again functions to exert a restoring force to the control in opposition to the pilots pressure. It will therefore be seen that the electrical servo system is sensitive to even small displacementsof the control, particularly in the case of high simulated airspeeds, thus providing realistic control feel within a comparatively small radius of movement about the neutral position.

- If the pilot horses the controls, i. e., moves them in a rapid and violent manner, the control feel is still retained by reason of the velocity and acceleration voltage generators 65 and 68 which function in the manner previously described for eliminating overshooting or hunting and excessive inertia feel of the servo system. If, after a displacement of the control, the pilot suddenly lets go, the torque motor 63 returns the stick to neutral at substantially the same speed and with no more hunting than in thecase of the type of control simulated, this part'of the control being due to the velocity voltage generator 65 as graphically illustrated by Fig. 5.

Though but a single embodiment of the invention has been illustrated and described, -it is to be understood that the invention may be applied in various forms. Changes may be made in the arrangements shown without departing from the spirit or scope of the invention as will be apparent to those skilled in the art and reference should be made to the appended claims for a definition of the limits of the invention.

What is claimed is:

l. Simulating apparatus for loading pilot-operated aircraft ight controls according to aerodynamic forces acting on said controls under different flight conditions comprising flight computing means responsive to the operation of said aircraft controls for producing control voltage representing a function of airspeed, means for loading a respective aircraft control comprising computing means for producing force control voltage which is varied according both to displacement of said aircraft control from neutral and Value of said airspeed function potential, means for transmitting a loading force to said aircraft control opposing the pilots force tending to move the control from neutral, said loading means being controlled according to said force voltage Vsuch that the loading force on said control for both static and dynamic conditions thereof is proportional to the magnitude of the existing force voltage and the direction of said force corresponds to the polarity or sense of said voltage, and feedback means sensitive to the dynamic operation of said control for modifying the effect on said loading means of said force control voltage-thereby to simulate control feeL Y 2.V Simulating apparatus for loading pilot-operated aircraft llight controlsV according to aerodynamic forces acting on said controls under diferentight conditions com prising means for representing' airspeed, means for loading a respective aircraft control comprising 'force compnting means for producing force control voltage responsive jointly to displacement of said aircraft control from neutral and the represented airspeed, loading means including electric power means for transmitting a loading force to said aircraft control for opposing the pilots force tending to'move the control from neutral, said loading means being controlled according to said force voltage such that the loading force on said control for both static and dynamic conditions of the control is proportional to the magnitude of the existing force voltage and the direction of said force corresponds to the polarity or sense of said voltage, and electrical feedback means sensitive to the dynamic operation of said control for modifying the eect on said loading means of said force control voltage thereby to simulate control feel incident to displacement of said control.

3. Simulating apparatus for loading pilot-operated aircraft flight controls according to aerodynamic forces acting on such controls under different flight conditions comprising means for representing airspeed, means for loading a respective aircraft control comprising force computing means for producing force control voltage according to displacement of said aircraft control and the represented airspeed, loading means including an electric motor for transmitting a loading force to said aircraft control for opposing the pilots force tending to move the control from neutral, said loading means being controlled according to the magnitude and sense of said force voltage for both static and dynamic conditions of the control, and electrical means sensitive to the dynamic operation of said control for producing feedback voltage for energizing said force computing means so as to modify the elect on said loading means of said force control voltage thereby to simulate control feel 'incident to displacement of said control.

4. Simulating apparatus for loading pilot-operated air craft flight controls according to aerodynamic forces acting on such controls under different ght conditions com prising means for representing airspeed, means for loading a respective aircraft control comprising electric power means for transmitting a loading force to said aircraft control for opposing the pilots force tending to move the control from neutral, means for energizing said electric power means according both to displacement of said aircraft control and the represented airspeed so that said power means impresses a loading force -on said control for both static and dynamic conditions thereof, and electrical means sensitive to the dynamic operation of said control for producing feedback voltage for controlling said electric power means so as to modify the operation thereof and thereby simulate control feel incident to displacement of said control.

5. In grounded llight training apparatus having simulated aircraft controls operable by a student pilot and flight computing means for producing a control quantity representing a function of airspeed responsive to the operation of said aircraft controls, means for loading a respective control in simulation of flight conditions comprising means energized by said airspeed control quantity and variable by means of said respective control for deriving a force control quantity which varies in accordance with the movement of said respective control, said force quantity representing joint effects of control dis placement and simulated airspeed, a torque motor hav ing a rotatable element connected to said respective control and responsive to said force quantity for directly resisting displacement of said control from its neutral position, and feedback means sensitive to the dynamic operation of said torque motor for modifying the effect of said force control quantity on said motor to simulate control feel 6. In grounded flight training apparatus having simulated aircraft controls operable by a student pilot and llightcomputing means for producing a control voltage representing a Afunction of airspeed responsive to the operation of said aircraft controls, means for loading a respective control in simulation of Hight conditions `compris'ing means energized by said airspeed voltage and variable by means of said respective control forderiving a force control voltage which varies in accordance with the movementof said respective control, said force voltage representing joint elfects of control displacement and simulated airspeed, amplifying means energized by said forcevoltage, a torque motor having a rotatable element connected to said respective control and energized according to the amplified voltage for directly resisting displacement of said control from its neutral position, and feedback means sensitive to the dynamic operation of said torque motor for modifying the effect of said force control voltage on said motor to simulate control feeL 7. In grounded Hight training apparatus having simulated aircraft controls operable by a student pilot and Hight computing means for producing control potential representing a function of airspeed responsive to the operation of said aircraft controls, means for loading a respective control in simulation of Hight conditions comprising means energized by said control potential and variable by means of said respective control for deriving force control potential which varies in accordance with the movement of said respective control, said force potential representing joint effects of control displacement and simulated airspeed, a torque motor having a rotatable element connected through a non-yielding connection to said respective control and responsive to said force potential for directly resisting displacement of said control from its neutral position, and feedback means sensitive to the dynamic operation of said torque motor for modifying the eHect of said force control potential on said motor to simulate control feel 8. In grounded Hight training apparatus having simulated aircraft controls operable by a student pilot and Hight computing means for producing control potential representing a function of airspeed responsive to the operation of said aircraft controls, means for loading a respective control in simulation of flight conditions cornprising means energized by said control potential and variable by means of said respective control for deriving force control potential which varies in accordance with the movement of said respective control, said force potential representing joint effects of control displacement and simulated airspeed, a torque motor having a rotatable element connected to said respective control and responsive to said force potential for directly resisting displacement of said control from its neutral position, and feedback means sensitive to the dynamic operation of said torque motor comprising velocity and acceleration sensing means for producing respective potential for jointly modifying the effect of said force control potential on said motor to simulate control feel 9. In grounded Hight training apparatus having simu` lated aircraft controls operable by a student pilot and Hight computing means for producing control quantities responsive to the operation of said aircraft controls, means for loading said controls in simulation of Hight conditions comprising means energized by one of said control quantities representing airspeed and variable by movement of a respective control for deriving a force control quantity which varies in response to the movement of said respective control, said force quantity representing joint effects of control displacement and simulated airspeed, means jointly responsive to said force control quantity and to other control quantities representing other aerodynamic factors produced by said Hight computing means for producing a resultant control quantity representing the resultant of aerodynamic forces acting on said control, a torque motor having a rotatable element connected to said control and energized according to said resultant control quantity for resisting displacement of said control from its neutral position, and feedback means responsive to the dynamic operation of said 10 torque motor for modifying the effect of said resultant control quantity to simulate control feel 10. Ingrounded Hight training apparatus having simulated aircraft controls operable by a student pliot and Hight computing means for producing control voltages representing Hight conditions responsive to the operation of said aircraft controls, means for loading said controls in simulation of Hight conditions comprising means energized by one of said control voltages representing airspeed and variable by movement of a respective control for deriving a force control Vvoltage which varies in response to the operation of said respective control, said force voltage representing joint effects of control displacement and simulated airspeed, means jointly responsive to said force control voltage and to other of said concontrol voltages representing other Hight conditions produced by said Hight computing means for producing a resultant control voltage representing the resultant of aerodynamic forces acting on said control, a torque motor having a rotatable element connected to said control, said torque motor being energized according to said resultant voltage for resisting displacement of said control from its neutral position, and feedback means responsive to the dynamic operation of said torque motor for sensing dynamic changes and producing potential for modifying the effect of said resultant control voltage to simulate control feel 1l. In grounded Hight training apparatus having simulated aircraft Icontrols operable by a student pilot and Hight computing means for producing control quantities responsive to the operation of said aircraft controls, means for loading said controls in simulation of Hight conditions comprising means energized by one of said control quantities representing a function of airspeed and variable by movement of a respective control for deriving a force control quantity which varies in response to the movement of said respective control representing joint elects of control displacement and simulated airspeed, means jointly responsive to said force control quantity and to other control quantities representing other aerodynamic factors produced by said Hight computing means for producing a resultant control quantity representing the resultant of aerodynamic forces acting on said control, a torque motor having a rotatable element connected to said control through a non-yielding connection and energized according to said resultant control quantity for resisting displacement of said control from its neutral position, and velocity and acceleration sensing means responsive to the dynamic operation of said torque motor for jointly modifying the effect of said resultant control quantity to simulate control feel l2. In grounded Hight training apparatus having simulated aircraft controls operable by a student pilot and Hight computing means for producing control voltages representing Hight conditions responsive to the operation of said aircraft controls, means for loading said controls in simulation of Hight conditions comprising means energized by one of said control voltages representing a function of airspeed and variable by movement of a respective control for deriving a force control voltage which varies in response to the operation of said respective control representing joint etlfects of control displacement and simulated airspeed, means jointly responsive to said force control voltage and to other control voltages representing other aerodynamic factors produced by said Hight computing means for producing a resultant control voltage representing the resultant of aerodynamic forces acting on said control, an electric torque motor having a rotatable element connected to said control, said torque motor being energized according to said resultant voltage for resisting displacement of said ycontrol from its neutral position, velocity sensing' means and acceleration sensing means each responsive to the operation of said rotatable element for producing respective volt- Y 11 agesv for jointly modifying the effect of said vresulta-nt control .voltage to simulate control feeL l I 13. In grounded flight training apparatus having simulated aircraft controls Yoperable by a student pilot and flight computing means for producing control quantities responsive to the operation of said aircraft controls, means for loading said controls in simulation of flight conditions comprising means energized by one of said control quantities representing a function of airspeed and variable by movement of a respective control for deriving a force control quantity which varies in response to the movement of said respective control representing joint effects of control displacement and simulated-airspeed, means jointly responsive to said force control quantity and to other control quantities representing other aerodynamic factors produced by said flight computing means for producing a resultant control quantity representing the resultant of aerodynamic forces acting on said control, a low power, low inertia torque motor having a rotatable element directly connected through torque converter means to said control and energized according to said resultant control quantity for resisting displacement of said control from its neutral position, and feedback control means responsive to dynamic operation of said torque motor adapted to sense motor dynamic changes for modifying the eifect of said resultant control quantity to simulate control feel 14. In grounded flight training apparatus having s'imulated aircraft controls operable by a student pilot and llight computing means for producing control voltages representing flight conditions responsive to the operation of said aircraft controls, means for loading said controls in simulation of flight conditions comprising means energized by one of said control voltages representing a function of airspeed and variable by movement of a respective control for deriving a force control voltage which varies in response to the operation of said respective control representing the joint effects of control displacement and simulated airspeed, means jointly responsive to said force control voltage and to other control 40 voltages representing other aerodynamic factors produced by said flight computing means according to the respective control simulated for producing a resultant control voltage representing the resultant of aerodynamic forces acting on said control, a torque motor having a rotatable element directly connected through torque converter means to said control, said torque motor being energized according to said resultant voltage for resisting displacement of; said control from its neutral position, and velocity sensing means responsive to the operation of said torque motor for producing potential for modifying the effect of said resultant control voltage so as to damp the operation of said motor for simulating control feel 15. ln grounded flight training apparatus having simulated aircraft controls operable by a student pilot and flight computing means for producing control quantities responsive to the operation of said aircraft controls, means for loading said controls in simulation of flight conditions comprising means energized by one of said control quantities representing a function'of airspeed and variable by movement of a respective control for deriving a force control quantity which varies in response to the movement of said respective control representing joint effects of control displacement and simulated airspeed, means jointly responsiveto said force control quantity and to other control quantities representing other aerodynamic factors produced by said flight computing means according to the respective control simulated for producing a resultant control quantity representing the resultant of aerodynamic forces acting on said control, a low power, low inertia torque motor having a rotatable element, a hydraulic torque converter mechanism directly interconnecting said rotatable element and said control, said motor being energized according to said resultant quantity for resisting displacement of said control from its neutral position, and means responsive to the dynamic operation of said motor, adapted to sense motor velocity and aeceleration for modifying the effect of said resultant quantity to simulate control feeL References Cited in the le of this patent UNITED STATES PATENTS 

